Glass because of its natural beauty, sleekness, and transparency is desirable for use as cover glass for displays in mobile (or portable) electronic devices. However, mobile electronic devices because of their mobile nature, and often small size, are prone to accidents that can cause glass to become scratched, chipped, or broken. For cover glasses to find wide use in mobile electronic devices, they would need to be tough and resistant to damage.
“Glass under load deforms elastically until sudden failure is initiated at a surface flaw under high stress” (W. A. Dalgliesh and D. A. Taylor, “The Strength and Testing of Window Glass,” Canadian Journal of Civil Engineering, Vol. 17, No. 5, October 1990, p. 753). To increase the threshold for sudden failure, glass is often subjected to a thermal or chemical strengthening process. These strengthening processes place the glass surface in compression, thereby increasing the amount of load that can be applied to the glass before the glass fails.
Prior to strengthening, the glass is particularly susceptible to damage, which may occur when a solid (or hard) object touches the glass. The damage to the glass may include surface flaws such as scratches and nicks, which would become failure sites under high stress. The surface flaws in the glass typically persist after the glass has been subjected to the strengthening process. Tiny surface flaws, e.g., with sizes less than 5 μm, have been found to adversely impact the performance of a strengthened glass as measured by a ball drop test.